A heat exchanger typically has a metal tube with fins extending radially away from the metal tube to increase the surface area which facilitates heat transfer. These fins are often called spiral fins and include a narrow aluminum strip that is helically wound to the metal tube, preferably the edge of the strip is secured to the tube. See FIG. 1 for a heat exchanger 10 in accordance with the prior art. FIG. 1 shows tube 12, fin 14, and edge 16 of fin secured to tube 12. The strip is usually fixed to the tube either by inserting it into a scored groove or by forming a small L at the base of the fin, which is then secured to the tube. See FIG. 2.
Because the fin is often bent about the tube to form the fin, particularly a fin having a rectangular cross section, it has commonly been believed that there is a large compressive force at the base of the fin and a large tensile force at the tip of the fin. This may be the rationale for traditionally manufactured fins to utilize a malleable material so that it may be formed and bent about a tube. Moreover, traditionally manufactured fins typically used a thermally conductive material so that it may be able to transfer heat.
Further, traditional methods for providing a fin often included the use of a stretchable material, the higher the ductility or elongation percentage the better. Hence, a fully annealed aluminum was normally used to provide fins. Additionally, the fully annealed aluminum often has at least a 30% elongation, a characteristic of the aluminum commonly specified within the spiral fin heat exchanger industry. Generally, aluminum of at least 99.00% purity is used for spiral fins because this offers enhanced thermal conductivity. 99% purity means the alloy has a minimum of at least 99% aluminum.
As a result, traditional fins, although having enhanced thermal conductivity, have been extremely soft and prone to damage during manufacture, handling, installation, and maintenance of the finned tubes. During servicing, fins are commonly cleaned using high-pressure air or water and the fins may bend as a result of the cleaning, in which case the fins may need to be repaired. The repair costs and down time often exacerbates the problem, especially when the repairs are needed each time the fins are cleaned. In the alternative, some users do not clean or repair the fins. However, debris on the fins or using distorted fins may reduce the heat-transfer capacity of the heat exchanger, and reduce the life of the fins or heat exchanger.
What is desired, therefore, is a fin that maintains the benefits of the traditionally made fins while reducing the disadvantages of the traditionally made fins. Another desire is a fin that resists distortion without a decrease in thermal conductivity. A further desire is a fin that resists damage without sacrificing needed flexibility to be maneuvered about the tube.